SQLite pool implementation. Maintains N pre-opened esqlite3 database connections in an ETS-tracked free list. Each checkout/2 hands out a connection; checkin/2 returns it.

Pool state

One ETS table per pool, named after the pool atom. Holds:

• {available, [esqlite3:esqlite3()]} - free connections.
• {checked_out, #{esqlite3:esqlite3() => pid()}} - leased + owner.
• {db_path, binary()} - the database path or :memory: URI.

pool_size from start_pool/2 opts pre-opens N connections.

Example

{ok, _Pid} = kura_pool_sqlite:start_pool(my_pool, #{
    database => <<":memory:">>,
    pool_size => 4
}).

Notes vs PG

Unlike pgo's holder-ETS pattern, SQLite has no socket and no server, so a connection is simply an open database handle. The pool's only job is bounding the count of simultaneously open handles and pairing checkout with checkin.